The present invention relates to an apparatus for processing or observing a semiconductor wafer with a charged particle beam.
Along with advances in the level of integration and in the design rule of semiconductor devices, a micro processing/observing technology is being requested also in the defect analysis of the semiconductor devices. As a micro processing/observing technology for a defect in a semiconductor device, a cross-section observing method, for example with an FIB-SEM apparatus, of forming a cross section by an etching with an FIB and observing the cross section with an SEM is disclosed (for example cf. Patent Reference 1).
In case of a cross-sectional observation of a sample with an FIB-SEM apparatus, as the cross section formed by a focused ion beam is observed by an irradiation with an electron beam, a sample stage has to be regulated to be at such a height that the focused ion beam and the electron beam are focused on a same observation point (eucentric position) of the sample. Unless the height of the sample stage is regulated, the cross-sectional part formed by the focused ion beam may not be contained in an irradiating range of the electron beam and the sample stage may have to be displaced for observing the cross section, thereby deteriorating the efficiency of operation. Therefore, following procedure has been employed for regulating the height of the sample stage. A specified position on the sample is scan-irradiated with a charged particle beam to obtain a secondary electron image. Then the sample stage is inclined, and a scan-irradiation with a charged particle beam is executed in the inclined state to obtain a secondary electron image. A displacement amount of the specified position in thus obtained secondary electron image, from the specified position in the secondary electron image obtained prior to inclining, is determined, and the height of the sample stage is regulated so as to decrease the displacement amount (for example cf. Patent Reference 2).
However, a wafer of a diameter of 300 mm is recently introduced into the semiconductor process, and a sample of a large diameter such as a 300 mm wafer, may generate a bending in a height direction of the sample. In such case, since the sample height varies even within a same wafer, a focused ion beam and an electron beam may not be focused on a same observation point on the wafer in different positions of the wafer, even by a height regulation of the sample stage.
Patent Reference 1: JP-A-11-213935
Patent Reference 2: JP-A-2000-251823
A process of defect analysis requires an improvement in the throughput and in the precision of observation associated with a miniaturization of a part to be analyzed, and it is desired that observation and processing can be executed easily within a short time and with a high precision.
However, in the above-described method of sample height regulation based on an image displacement amount by inclining the sample, the operation efficiency is low because the sample has to be inclined. Also in case that the sample is bent in a height direction thereof as in a case of a 300 mm wafer, the operation efficiency may be lowered because the precision of observation and processing is lowered, or because the sample stage has to be displaced every time when switching between observation and processing.
The present invention is to solve such problems in the prior method and apparatus, and an object thereof is to enable observation and processing precisely and easily within a short time.